Light and heat sensitive sheet material

ABSTRACT

Photosensitive sheet material is described which produces sharply defined dense images on a transparent background simply by exposure to a light-image followed by heating.

limited States Patent [191 Wiese Jr. et a1.

[ 51- Oct. 30, 1973 [54] LIGHT AND HEAT SENSITIVE SHEET MATERIAL [7 5} Inventors: Joseph A. Wiese Jr.; George Van Dyke Tiers,both of St. Paul; George B. Rathmann,North Oaks, all of Minn.

[2]] Appl. No.: 732,863

[52] U.S. Cl. 96/84 R, 96/68 [51] Int. Cl G03c 1/84, G036 5/00 [58] Field of Search 96/67, 84

[56] References Cited UNITED STATES PATENTS 2,770,534 11/1956 Marx ..96/5

Primary Examiner-N0rman G. Torchin Assistant ExaminerAlfonso T. Suro Pico Attorney-Alexander, Sell, Steldt and Delahunt [5 7] ABSTRACT Photosensitive sheet material is described which produces sharply defined dense images on a transparent background simply by exposure to a light-image followed by heating. 1

11 Claims, N0 Drawings LIGHT AND HEAT SENSITIVE SHEET MATERIAL This invention relates to the recording of light-images and to sheet materials useful therein.

Sheet materials have been described on which visible images are easily and rapidly developed by first exposing the sheet to a light-image and then briefly subjecting the exposed sheet to moderately elevated temperature. As described in U.S. application Ser. No. 693,714, now US. Pat. No. 3,457,075, such a dry photography or dry silver sheet may comprise photosensitive silver halide catalyst-forming means in catalytic proximity with major proportions of organic silver salt oxidizing agents and reducing agents for silver ion as heat-sensitive reactant image'forming means. When applied to transparent substrates, these compositions produce light-sensitive sheet materials of surprisingly high transparency which exhibit almost no lightscattering tendency and have been found capable of forming exceedingly sharply outlined images.

The full capability of high resolution and sharp outline of the non-light-scattering coatings just described cannot be realized where internal reflection, for example at the interface between coating and substrate, is present. The introduction in the light-sensitive coating of light-absorbing components to eliminate the reflected rays is undesirable since some of the useful rays also are unavoidably absorbed. The addition of lightabsorbing or antihalation coatings which must subsequently be chemically decolorized or physically removed, as is commonly practiced in conventional photography, is equally undesirable since much of the ad vantage of simplicity of processing is thereby lost.

it has now been found possible to incorporate, in the transparent light-sensitive heat-developable sheet materials hereinbefore described, light-absorbing or antihalation components or layers which greatly reduce or eliminate the adverse effects of internal reflection while retaining the full advantages of rapid and uncomplicated processing. Images of excellent sharpness or acutance are achieved, without any lossof speed or sensitivity, on simply exposing the sheet to the lightimage and then heating to develop the visible image. One important result is that it has been found possible to provide, by extremely rapid and time-saving procedures, microfilm transparencies with which images of excellent resolution may be projected at high levels of magnification.

These and other advantages are obtained, in accordance with the principles of the present invention, through the inclusion of a light-absorptive layer which loses its light-absorptivity and becomes essentially transparent when heated.

A preferred structure consists of a thin transparent support or carrier coated with a colored heatbleachable first layer and with a transparent lightsensitive heat-developable dry silver second layer. The sheet is exposed to a light-image. Light rays passing through the light-sensitive layer are absorbed in the colored layer and are therebyprevented from being reflected back into the sensitive layer, so that completely controlled exposure is attained. The sheet -is then heated to develop the visible image in the second layer. The heating simultaneously causes discharge of the color in the colored first layer, so that non-image areas of the developed print are transparent. The image areas are sharply outlined; halation is reduced or eliminated.

The invention is not restricted to light-sensitive dry silver sheets, but is applicable also with conventional wet-process silver halide photographic films and other light-sensitive sheet materials. As an example, a photographic film in wich is incorporated a color layer as herein described may be exposed to a light-image, de-

veloped by the wet process, washed, and then simultaneously dried and decolorized by heating to provide an essentially halation-free transparency.

The invention furthermore is not to be restricted to sheet materials which on heating are converted from visual opacity to full visual transparency. Depending on the formulation of the photosensitive layer as influenced by the uses for which the sheet is designed, the color layer may be made highly selective in its lightabsorbing properties or may absorb over a wide spectrum; and the sheet after heat treatment'may likewise be visibly clear and transparent or may be transmissive only of certain restricted wavelengths. The significant requirements are that the heat-sensitive layer be absorptive of rays which affect the photo-sensitive layer, and that it be converted by heat to a form in which it no longer absorbs those rays or other rays for which unimpeded transmission is required. However the color layers which become completely colorless, clear and transparent when heated are of most general utility and are ordinarily preferred.

Color-bodies or color layers which absorb light of desired wavelength and which are bleached or decolorized by moderate heating under conditions which do not degrade the remaining components of the sheet are generally useful in the practice of the invention. Many organic dyes possess the required combination or properties or may be appropriately treated to achieve them, are available in desired shades and colors, and are presently preferred; but many other heat-bleachable colorbodies are also useful. As one example may be mentioned those color-bodies characterized as color center crystals, such for example as alkali halide crystals which have been subjected to electron bombardment.

In a presently preferred form, the invention makes use of organic dyes which are decolorized either by decomposition with removal of an acidic component or by reaction of a base with the acidic dye, in either case leaving an essentially colorless residue. The acid removed may be retained within the film and may then slowly recombine with the chromogen to re-form the color; or it may convert to a less reactive material, such as an anhydride, which is incapable of recombination and color formation; or it may react with an acid acceptor component initially present, or preferably formed by heat decomposition of another component of the color layer, so as no longer to be available for reaction. Alternatively and less desirably, the acid component of the dye may be neutralized by reaction with a basic material which by heating is caused to migrate from a closely adjacent position into reactive contact with the color material. In allcases the color is removed by heating. 7

The heat-bleachable colored layer may be applied as an external coating but is most effective as a subbing layer between the light-sensitive coating and the transparentfilm base. Light rays passing through the lightsensitive coating are absorbed and are prevented from being reflected at the surfaces of the base and thence returning to the sensitive coating. Colored coatings which must be decolorized by extraction or by reaction with components of a developing or fixing bath are not easily decolorized when in such position, since they are necessarily not readily accessible to the solutions.

The colored material may alternatively be incorporated directly within the film base. In the case of soluble or externally reactive materials and water-resistant films, such a structure would completely prevent any subsequent decolorization by the customary methods of extraction or chemical bleaching using liquid processing solutions.

The present invention therefore makes possible the maximum reduction of blurring caused by internal reflection in a light-sensitive film structure while still permitting the attainment of full transparency and absence of color at non-image areas and with a minimum of processing.

The color layer may less desirably be placed in an exposed position and the color removed by heat-induced reaction with reactant materials from external sources. Although halation is less effectively reduced by such structures, the simplicity of the method still provides advantages over conventional wet processes.

The light-stable heat-transparentizable colored film base and color-coated film base sheet materials are useful not only as supports for light-sensitive coatings as already described but alsoas color projection transparency sheets which may be imaged by heating at imagedefining areas. As an illustration, the color-coated film is held in heat-conductive pressure-contact with a printed original which is then briefly exposed to high intensity infra-red radiation to produce a heating effect at the radiation-absorptive printed image areas and to decolorize corresponding areas of the colored film, which is then useful as a projection transparency.

The following specific Examples will serve further to illustrate but not to limit the invention.

EXAMPLE 1 A sheet of 1' mil transparent Mylar polyester film is uniformly coated over one surface with a mixture of 0.02 gram of N-(bis (4-dimethylaminophenyl) methyl) pyrrolidine, (available under the trade designation National Aniline Color Precursor No. l), and 0.07'gram of salicylic acid in ml. of a 10 percent solution of polyvinyl acetate in Z-butanone, and the coating is dried. The dry residue is approximately one-tenth mil in thickness and is of deep cyan color.

Over the dried coating there is provided a transparent light-sensitive heat-developable coating of the type described in US. application Ser. No. 693,714 and containing photo-sensitive silver bromide catalystforming means in catalytic proximity with heatsensitive reactant image-forming means comprising silver behenate and hydroquinone in polyvinyl butyral resin binder. A small proportion of spectral sensitizing dye is desirably included but is not essential. The dry light-sensitive coating weighs approximately 1 gram per square foot.

The light-sensitive sheet is next exposed at its coated surface to a light-image and is then uniformly heated to develop a visible image. The exposure time and intensity, and the time and temperature of heating, are selected on the basis of preliminary trials to provide optimum contrast between image and non-image areas. Characteristic conditions include exposing to light at maximum intensity of not more than about 180 footcandle-seconds and heating for about two seconds at about 220F.

The resulting print is a dense black at fully exposed areas and is clear and transparent at unexposed or background areas. The edges of the image areas are sharp and clear-cut. Halation' is substantially completely eliminated.

A sensitive sheet prepared in the same manner ex- 1 cept for omission of the colored intermediate layer and similarly exposed and developed produces image areas of equal density but having fuzzy and indistinct edges.

Analogous results are obtained by substituting for the color-forming components of Example 1 the following materials: N-(n-butyD-N'-(bis-(4-dimethylaminophenyl)- methylene)-urea (0.1 g.) and dichloromaleic acid (0.002 g.); Color Precursor No. 1 (0.2 g.) and dichloromaleic acid (0.07 g.); Genacryl Yellow 5GP (Color Index 48065) (0.065 g.) and 2 drops of saturated aqueous solution of tetraethylammonium cyanoacetate adjusted to pH between 4 and.8 by addition of cyanoacetic acid (Solution A); Genacryl Yellow 30 (CI 48055) (0.065 g.) and 2 drops of Solution A; Genacryl Red 68 (CI48020) (0.065 g.) and 2 drops of Solution A; Genacryl Orange R (CI 48040) (0.065 g.) and 2 drops of Solution A; Genacryl Orange 60 (Cl 48- 035) (0.065 g.) and 2 drops of Solution A; Genacryl Orange 66 (0.033 g.) and 3 drops of Solution A. The several colors available make possible the selection of a particular color so as to obtain best possible results with an image layer having maximum sensitivity at a particular range of wavelengths, as obtained with an appropriate selection of spectral sensitizer. Other polymeric film-forming binders, e.g., as illustrated in the other Examples, may be substituted for the polyvinyl acetate.

Decolorization of the color layer under the conditions defined is complete with each of the color components listed; but in some instances and under certain conditions the color may slowly reappear. Stability of the decolorized layer may be only a few hours with the salicylic acid formulas, but is much greater with the combinations containing dichloromaleic acid and is essentially permanent with the compositions employing the tetraethyl-ammonium cyanoacetate. The less stable structures retain their transparency for a period sufficient to permit their use as negatives in the preparation of positive prints but are less desirable where they are to be retained for long periods.

EXAMPLE 2 A base film is prepared, by casting on a smooth polished release surface, from a solution of Color Precursor No. 1 (0.2 g.) and dichloromaleic acid (0.07 g.) in 30 ml. of a 10 percent solution of cellulose acetate in methylethylketone. The dried film is about 2 mils thick and is a deep cyan in color. The film is further coated with a transparent lightsensitive heat-developable coating as described in Example 1. Exposure to a lightimage followed by heat development produces a dense black image and decolorizes the base film. The edges of the image are sharp and clear-cut, with essentially no halation.

EXAMPLE 3 Two mil transparent Mylar polyester film is coated with a solution containing 4,4'-methylenebis-N,N-

dimethylaniline (0.1 g.), VYHH vinyl chlorideacetate copolymer (0.5 g.), and polyvinylacetate (0.5 g.) in methylene chloride ml.), applied at a wet thickness of 3 mils. The colorless dried coating is exposed to an ionizing radiation and converts to a cyan color. A further coating of transparent light-sensitive heat-developable dry silver material is applied, and the sheet is exposed to a light-image and heated to develop the visible image and decolorize the sub-coat. The edges of the image are sharp and clear-cut; halation is almost completely eliminated.

EXAMPLE 4 Two mil polyester film is coated with a heatbleachable cyan layer as described under Example 1 and which is then over-coated with about 0.1 mil of polyester resin applied from 10 percent solution in methylethylketone. Over the dry coating is next applied a conventional silver-halide-gelatin light-sensitive photographic emulsion. The dry sheet is exposed to a lightimage and the latent image is developed, fixed and washed by conventional methods employed with such emulsion coatings. There is produced a print having a dense black image on a cyan background. The still damp print is dried on a photographic print drier by holding for about one minute against the surface of a polished metal drum maintained at 240F. The colored layer is rendered clear and colorless. A sharply defined image is obtained, .with very little halation.

The ketone-soluble polyester resin'layer provides a receptive sub-coat for the photographic emulsion. The sub-coat may be eliminated while still obtaining excellent emulsion coatability by substituting the ketonesoluble polyester resin for the polyvinyl acetate binder component in the heat-bleachable color coat, with appropriate change in solvent. The integrity of the coated film is improved and the edge sharpness of the iamge areas is also improved.

EXAMPLE 5 Transparent base film is coated witha first layer of Color Precursor No. 1 (0.045 g.), Color Precursor X- 4405 (0.055 g.), salicylic acid (0.07 g.) and polyvinyl chloride-acetate (1.0 g.) all dissolved in 10 ml. of methylethylketone, at a wet coating thickness of 3 mils. A second thin coating of hexadecyldimethyl-amine (0.1 g.) and ethyl cellulose (0.5 g.) in methylethylketone 10 ml.) is applied over the green-colored dried coating and the sheet is again dried. A further transparent lightsensitive heat-developable coating as described under Example 1 completes the structure. Exposure to a lightimage followed by heating develops a well-defined and essentially halation-free black image in the lightsensitive layer and permanently decolorizes the color layer.

Color Precursor X-4405 has the structural formula a yellow dye.

EXAMPLE 6 Transparent base film is supplied with a first coat of polyvinyl butyral containing silver behenate which has been treated with halide ion to convert a small portion of the silver into light-sensitive silver halide, a second coat of polyvinyl acetate to which has been added equal parts by weight of N-(n-butyl)-N-(bis(4- dimethylaminophenyl)- methylene )-urea and dichloromaleic acid forming a magenta color, and a third coat of polyvinyl butyral containing hydroquinone in amount sufficient to reduce the silver ion content of the first coating to metallic silver. The combination of first and third coats constitutes a lightand heat-sensitive dry silver coating. The sheet is exposed to a lightimage and heated. A sharply defined essentially halation-free black image is developed in the first coat and the color of the second coat is discharged.

EXAMPLE 7 A solution of X-4405 color precursor (0.1 g.) and salicylic acid (0.07 g.) in 10 ml. of a 10 percent solution of vinyl chloride-acetate copolymer in methylethylketone is applied as a first coating to transparent film base and dried. The opposite surface of the base is supplied with a transparent light-sensitive heatdevelopable dry silver coating. A second portion of film base is separately coated with a solution of hexadecyldimethylamine (0.45 g.) and ethyl cellulose (0.05 g.) in methylethylketone 10 ml.), and dried. The first sheet is exposed to a light-image. The second sheet is then placed with its coated surface against the colored surface of the first sheet and the composite is heated at a temperature and for a time sufficient to develop the image to maximum contrast. The yellow color is simultaneously permanently discharged. A sharply defined and substantially halation-free image is obtained.

EXAMPLE 8 Two mil transparent Mylar polyester film is coated with a solution of 0.15 part by weight of yellow dye in 5 parts of a2 percent solution of polyvinyl alcohol in water, applied at a wet coating thickness of 1 mil and dried at room temperature. The dye is identified as 2.5- dimethoxy-4-(4-methyl-phenyl)- thiobenzenediazonium fluoborate, having the structural formula O CH:

HaC

EXAMPLE 9 Two mil transparent Mylar polyester film is first supplied with a thin coating of a saturated aqueous solution of potassium chloride and the water is removed by evaporation, leaving an opalescent crystalline deposit. A thin coating of a percent solution in methyle thylketone of water-insoluble ketone-soluble transparent polyester resin is applied over the treated surface and dried; the resin re-transparentizes the sheet and serves to retain and protect the salt crystals. The sheet is exposed to X-rays, whereupon the salt layer is converted to a blue-violet color, and is then supplied with a photosensitive heat-developable dry silver coating comprising silver behenate, silver bromide, reducing agent, and polyvinyl butyral binder. The sheet is exposed to a light-image and then heated to develop thevisible image. Halation is minimized, the color is eliminated, and a transparency having sharp black images and a clear colorless transparent background is produced.

What is claimed is as follows:

1. Sheet material adapted for making accurate visible records of light-images and comprising a transparent support member, a transparent light-sensitive imageforming layer for recording said light-images, and a colored light-absorptive antihalation layer. which loses its light-absorptivity when heated.

2. Sheet material of claim 1 wherein said lightsensitive image-forming layer comprises silver halide.

3. Sheet material of claim 2 wherein said lightsensitive image-forming layer isheat-developable.

4. Sheet material of claim 3 wherein said lightsensitive image-forming layer includes a major proportion of organic silver salt oxidizing agent and reducing agent for silver ion.

5. Sheet material of claim 3 wherein said antihalation layer is heat-bleachable under the same timetemperature conditions required to heat-develop said light-sensitive image-forming layer.

6. Sheet material of claim 2 wherein said antihalation layer and said lightsensitive image-forming layer are in face-to-face contact.

7. Sheet material of claim 2 wherein said support member lies between said antihalation layer and said light-sensitive image-forming layer.

8. Sheet material of claim 2 wherein said color layer is included in said support member.

9. Sheet material of claim 4 wherein said antihalation layer comprises an organic dye.

10. Sheet material of claim 9 wherein said antihalation layer loses its light-absorptivity when heated under the same time-temperature conditions required to develop a visible image in the light-sensitive imageforming layer after exposure to a said light-image.

11. Sheet material of claim 1 wherein said transparent light-sensitive image-forming layer comprises photosensitive silver halide and said colored lightabsorptive antihalation layer comprises a colored organic dye which is decolorizable by decomposition with removal of an acidic component on heating. 

2. Sheet material of claim 1 wherein said light-sensitive image-forming layer comprises silver halide.
 3. Sheet material of claim 2 wherein said light-sensitive image-forming layer is heat-developable.
 4. Sheet material of claim 3 wherein said light-sensitive image-forming layer includes a major proportion of organic silver salt oxidizing agent and reducing agent for silver ion.
 5. Sheet material of claim 3 wherein said antihalation layer is heat-bleachable under the same time-temperature conditions required to heat-develop said light-sensitive image-forming layer.
 6. Sheet material of claim 2 wherein said antihalation layer and said light-sensitive image-forming layer are in face-to-face contact.
 7. Sheet material of claim 2 wherein said support member lies between said antihalation layer and said light-sensitive image-forming layer.
 8. Sheet material of claim 2 wherein said color layer is included in said support member.
 9. Sheet material of claim 4 wherein said antihalation layer comprises an organic dye.
 10. Sheet material of claim 9 wherein said antihalation layer loses its light-absorptivity when heated under the same time-temperature conditions required to develop a visible image in the light-sensitive image-forming layer after exposure to a said light-image.
 11. Sheet material of claim 1 wherein said transparent light-sensitive image-forming layer comprises photosensitive silver halide and said colored light-absorptive antihalation layer comprises a colored organic dye which is decolorizable by decomposition with removal of an acidic component on heating. 